Fluid Turbine Rotor Blade

ABSTRACT

A fluid turbine has semi-spherical, hollow blades arrayed about a vertical axis, and a passive wildlife-deterrent system using ultraviolet coloration of the rotor blades. The turbine&#39;s blade shape reduces drag on a convex side and increases drag on a concave side. Part of the center of the array of rotor blades is open, allowing flow through the center of the array. The spherical form enhances fluid flow through the center of the array and results in rotational force on a downwind blade, and directs fresh air into bypass flow.

TECHNICAL FIELD

The present disclosure relates to fluid turbines. Classifications might include “F03D3/0427, Wind motors with rotation axis substantially perpendicular to the air flow entering the rotor having stationary wind-guiding means, e.g. with shrouds or channels with augmenting action, i.e. the guiding means intercepting an area greater than the effective rotor area;” “G08G5/0095, Aspects of air-traffic control not provided for in the other subgroups of this main group;” and “F03D7/02—Controlling wind motors the wind motors having rotation axis substantially parallel to the air flow entering the rotor.”

BACKGROUND

In general, vertical-axis fluid turbines comprise arrays of vertical rotor blades arranged evenly about a central, vertical axis and coupled to an electrical generation machine. A Savonius turbine is commonly referred to as a drag-driven turbine. In this type of wind turbine, Some of the stream volume encounters a rotor blade on the downwind side of the vertical axis and some of the stream volume encounters a blade on the upwind side. The rotor blade shape reduces drag as the rotor moves against the wind on the upwind side of the rotor. When moving with the wind on the downwind side of the rotor, the shape of the rotor increases drag.

A datum plane is an imaginary surface from which measurements or locations are measured. Some examples of this embodiment refer to a non-planar surface as a datum surface. A datum sphere is an imaginary spherical surface connoting a measurement or location of objects in space that lie on the surface of a sphere.

Fluid turbines generate electricity from a fluid stream. One skilled in the art understands that air is a fluid and water is also a fluid. The aerodynamic principles that govern a wind turbine may function as hydrodynamic principles in a water turbine. In this disclosure example terms such as “wind” “fluid” and “stream” may be used interchangeably.

Generally, a fluid turbine captures energy from a fluid stream. As fluid flows from the upstream side of the rotor to the downstream side, the average axial fluid velocity remains constant as the flow passes through the rotor. Energy is extracted at the rotor, resulting in a pressure drop on the downstream side. The fluid directly downstream of the rotor is at sub-atmospheric pressure due to the energy extraction. The fluid directly upstream of the rotor is at greater-than-atmospheric pressure. The high pressure upstream of the rotor deflects some of the upstream air around the rotor, diverting a portion of the fluid stream around the open rotor as if by an impediment. As the fluid stream is diverted around the open rotor, it expands. This is referred to as flow expansion at the rotor.

According to Betz's Law, a maximum 59% of the total energy in a column of wind may be extracted by an open-rotor turbine. As a wind turbine extracts energy from a column of wind, the wind in the wake of the rotor plane slows down, creating relatively lower air pressure and lower energy flow in the wake. The low-pressure, low-energy air impedes the column of wind in its approach. As a result, some of the wind flows around the rotor blades. This is known as bypass flow. Bypass flow contains energy that cannot be captured by the turbine. The more energy extracted by a wind turbine, the more impediment is encountered. This, in general, is the reason only 59% of wind energy can be captured.

A fluid-turbine power coefficient is the power generated divided by the ideal power available by extracting all the wind's kinetic energy approaching the rotor area. It is commonly known that rotor wake affects rotor intake. A volume of fluid encounters a rotor as an impediment in part because a portion of the fluid flowing around the rotor expands in the wake of the rotor in a form referred to as stream volume.

Bypass flow passes over the outer surface of the stream volume. The amount of energy extracted from the stream volume creates slower-moving flow in the rotor wake, impeding flow through the rotor. This impediment increases the volume of the rotor wake. As more power is extracted at a rotor, the rotor stream volume will expand and more fluid flow will bypass the rotor. If a significant amount of energy is extracted, most of the fluid flow will bypass the rotor and the rotor can effectively stop extracting energy, a condition known as rotor stall. Thus maximum power is achieved from the two opposing effects: that of increased power extraction resulting in relatively lower flow rates, and that of reduced power extraction resulting in relatively higher flow rates. Greater efficiency can be achieved by increasing the speed of a rotor wake. Wake-flow velocity may be increased by injecting higher velocity fluid streams into the wake flow, thus allowing for increased power extraction at the rotor and providing a relatively greater coefficient of power.

SUMMARY

In an example embodiment, a Savonius-type vertical-axis wind turbine has a plurality of revolute blades arranged on its vertical axis. The blades' outer surfaces form a substantially spherical shape. Each of the revolute rotor blades captures air flow like any vertical turbine: perpendicular to the axis of rotation. The rotor blades are concave on their inner side and convex on their outer side, and arcuate at top and bottom surfaces, together forming a substantially spherical shape or datum sphere. This shape enables increased drag on the concave, inner side and reduced drag on the convex, outer side. The shape of the blades enables airflow through the center of the array, which is open. The ratio of open space in the center of the turbine to that of the rotor blades is between 1:5 and 1:7. A flow path through the substantially spherically shaped turbine blades increases in volume as it approaches the center of the sphere and decreases as it exits the sphere. Air flowing through a concave side of a first blade, through the open center and out along the concave surface of a second blade is also flowing through the spherical form and is therefore compressed at the exit as the flow path decreases in size.

A portion of the stream volume encounters a rotor blade on the downwind side of the vertical axis, and a portion of the stream volume encounters a rotor blade on the transverse, upwind side of the vertical axis. On the downwind side of the vertical axis, the convex side of each rotor blade faces upwind. An open center on the vertical axis allows some wind to flow through the turbine. The exhaust wind, having encountered the concave side of a rotor blade at a position referred to as θ=0°, continues through the center of the turbine and flows through a downwind blade, which is also referred to as a blade at position θ=90°, increasing the rotational velocity of the blade about the turbine vertical axis. Some of the wind that flows through an upwind rotor blade, otherwise referred to as a blade at θ=270°, flows through the center of the turbine and continues out through the concave side of a blade at position θ=270°, and out into the wake of the turbine, thus reducing the pressure on the back side of the upwind rotor blade. Injection of relatively higher speed air behind a rotor, minimizes wake pressure, reinforces the motion and reduces the pressure differential between the ambient flow and the wake.

The blades' substantially spherical shape causes air to flow into each subsequent blade portion by directing the flow toward the hollow center of the blade array and into the concave portion of the adjacent blade, which is in a downwind position. The spherical shape formed by the edges of each blade also serve to compress the exiting flow. This flow increases in velocity as it is compressed. The increased velocity allows more mass flow into the turbine, and helps dissipate the wake flow as it exits the turbine. Quicker wake-dissipation results in faster down-stream air recovery to ambient pressure. A reduced wake allows the turbines to be arranged more closely together in columns in a turbine field, improving efficiency.

In some embodiments, ultraviolet coloration of the rotor blades deters wildlife from approaching. Rotor blades are made of a composite-fiber-reinforced polymer with an ultraviolet reflective dye or laminated by an ultraviolet polymer film. The ultraviolet reflective surface appears fluorescent to birds but not to humans.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of an example embodiment;

FIG. 2 is a top, cross section flow diagram of the embodiment of FIG. 1;

FIG. 3 is a color diagram of the flow diagram of FIG. 2;

FIG. 4 is a side, cross section, flow diagram of the embodiment;

FIG. 5 is a color diagram of the flow diagram of FIG. 4;

FIG. 6 is an additional color diagram of the flow diagram of FIG. 4;

FIG. 7 is a front perspective view of a rotor blade of the embodiment;

FIG. 8 is a rear perspective view of a rotor blade of the embodiment;

FIG. 9 is a cutaway perspective view of the embodiment.

DESCRIPTION

In FIG. 1 rotor blades 110 are arrayed about a central axis 121. Each rotor blade's inner longitudinally oriented surface is concave 113 and each longitudinally oriented outer surface is convex 111. The concave inner surface 111 experiences increased drag in a fluid stream while the convex side 113 experiences relatively less drag. Latitudinally, each rotor blade has an upper surface 112 and a lower surface 114 which are both substantially perpendicular to the concave/convex surfaces 113/111. The upper surface 112 and lower surface 114 are coincident with a spherical datum surface.

The rotor blades 110 are connected to a shaft 117 that turns a generator 115. A housing 119 is located proximal to the rotor blades 110 and houses electronic controls. The apparatus is mounted on a base 123. The overall shape of the blades when assembled is that of a sphere. In an example embodiment, rotor blades are constructed of a fiber-reinforced polymer combined with a dye that appears fluorescent to birds and as monochromatic to humans.

The illustration in FIG. 2 is a top, cross-section view depicting flow through the turbine 100. The example embodiment shows four rotor blades 110, each having a concave side 113 and a convex side 111. One blade is at θ=0°, one at θ=90°, one at θ=180°, and another at θ=270°, One skilled in the art understands that the convex side 111 exhibits less drag when facing the fluid stream than a concave side 113. The rotor blade at θ=180°, while the concave side 113 exhibits greater drag when facing the fluid stream, causing rotation of the blades. In this view the apparatus is rotating in a clockwise rotation.

FIGS. 2 and 3 show a fluid stream meeting the turbine as an impediment, causing some of the stream 132 to flow past the turbine. This is referred to as bypass flow 132. The primary means of energy extraction occurs when fluid flows into the concave side of a blade 113, at position forming the resultant force vector 140. Some fluid streams flowing into the concave side of the blades at positions θ=270°, and θ=0°, are depicted by lines 136. Another portion of the fluid stream flows into the concave side of a blade at position θ=270 is shown as fluid stream 138. In one example, a portion of the fluid stream 136 and another portion of the fluid stream 138 encounters the concave side of a rotor blade at θ=270°, initially interacting with the concave side of the blade at θ=270°, creating the resultant force vector 144. The fluid then flows through the center of the turbine to the concave side of a rotor blade at position θ=90°, creating the resultant force vector 142. Some of the fluid 138 passes through the open center 139 of the turbine and creates a resultant force vector 142. Other portions of the fluid stream 134 flow through the center and out an upstream blade at θ=180°, creating force vector 146 before exiting the turbine to mix with bypass flow 132.

FIG. 4 is a flow diagram depicting a fluid stream moving through a vertical cross-section of the rotor blades. The spherical form of the rotor assembly guides the portion of the stream 136 through the open center of the rotor assembly. The portion of the fluid stream 136 is compressed as it passes through the turbine. Specifically, as it passes through the rotor assembly, some of the flow 136 becomes compressed, increasing in velocity. This compressed, higher-velocity fluid stream is depicted in dashed-line area 137. The higher velocity flow 137 then mixes with the relatively slower bypass flow 132 in the region of the turbine wake.

FIG. 5 shows a computer fluid-dynamics image of some of the wake flow 137 traveling at a relatively higher velocity than the surrounding wake flow 141. This is further supported by the image in FIG. 6.

FIG. 7 is a front perspective view of an example rotor blade 110 of the embodiment. The rotor blade 110 has a concave surface 113, a top surface 112 and a bottom surface 114. A space 116 is open in the center portion of the rotor blade 110. The top surface 112 and bottom surface 114 are coplanar. All four surfaces form a semi-spherical datum surface revolving around central axis 118.

FIG. 8 is a rear perspective view of an example rotor blade 110 of the embodiment. The rotor blade 110 has a convex surface 111, a top surface 112 and a bottom surface 114. A space 116 is open in the center portion of the rotor blade 110. A ratio between the area occupied by the open space 116 and the area occupied by the blade; made up of top surface 112, bottom surface 114 and convex/concave surface 111/113 (FIG. 8) is between 1:2 and 1:4 and in one embodiment is approximately 1:3. The top surface 112 and bottom surface 114 are coplanar. All four surfaces form a semi-spherical datum surface revolving around central axis 118.

FIG. 9 is a cutaway, perspective view showing the open center 116 and an example fluid stream line 136 creating force vectors 144 and 142 as it passes through the turbine. One skilled in the art understands how the flow diagram of FIG. 2 applies to the perspective view of FIG. 9. In some embodiments the ratio of open space in the center of the turbine to the area occupied by the rotor blades is between 1:5 and 1:7 and in one embodiment is approximately 1:6.

While example embodiments have been described herein, it is expressly noted that these embodiments should not be construed as limiting, but rather that additions and modifications to what is expressly described herein also are included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not made express herein, without departing from the spirit and scope of the invention. 

1. A rotor blade for a vertical axis fluid turbine comprising: a revolute surface with concave side and a convex side, a vertical edge and an edge that lies on the surface of a datum sphere; and a substantially vertical central axis parallel to the vertical edge through the center of said datum sphere; and a space between said vertical central axis and said vertical edge of said revolute surface; and a surface perpendicular to said revolute surface, engaged along said edge that lies on the surface of a datum sphere and coincident with said datum sphere; wherein fluid flowing over said concave side exerts a force about said central axis, and is compressed by said surface perpendicular to said revolute surface as the fluid moves off the surface.
 2. The rotor blade of claim 1 wherein the ratio of the volume of space between said vertical central axis and said vertical edge of said revolute surface and the volume surrounded by said revolute surface in combination with said surface perpendicular to said revolute surface is between 1:2 and 1:4.
 3. The rotor blade of claim 1 wherein the ratio of the volume of space between said vertical central axis and said vertical edge of said revolute surface and the volume surrounded by said revolute surface in combination with said surface perpendicular to said revolute surface is 1:3.
 4. A vertical axis fluid turbine comprising: a rotor assembly having at least two rotor blades; each rotor blade in said rotor assembly having a revolute surface bent to a concave side and a convex side, a vertical edge and an edge that lies on the surface of a datum sphere; and a substantially vertical central axis parallel to the vertical edge of said at least two rotor blades, said central axis extending through the center of said datum sphere; and a space between said vertical central axis and said vertical edge of said revolute surface on each of said at least two rotor blades; and each of said at least two rotor blades having a surface perpendicular to said revolute surface, engaged along said edge that lies on the surface of a datum sphere and coincident with said datum sphere; and each rotor blade in said rotor assembly having a semi spherical vertical cross section; wherein fluid flowing over one of said at least two rotor blades flows through said space between said vertical central axis and said vertical edges and then flows over another of said at least two rotor blades and is compressed by said surfaces perpendicular to said revolute surfaces as the fluid exits the rotor assembly.
 5. The vertical axis fluid turbine of claim 4 wherein the ratio of the volume of space surrounded by said vertical central axis and said vertical edge of said revolute surface on said at least two rotor blades, within said datum sphere, and the volume of said datum sphere is between 1:5 and 1:7; wherein said space is sufficient to allow fluid flowing over one of said at least two rotor blades to flow through said space and flow over at least one other of said at least two rotor blades, exerting a force on each of said at least two rotor blades.
 6. The vertical axis fluid turbine of claim 4 wherein the ratio of the volume of space between said vertical central axis and said vertical edge of said revolute surface on said at least two rotor blades within said datum sphere, and the volume of said datum sphere is 1:6.
 7. A vertical axis fluid turbine comprising: a rotor assembly having at least four rotor blades; each rotor blade in said rotor assembly having a revolute surface bent to a concave side and a convex side, a vertical edge and an edge that lies on the surface of a datum sphere; and a substantially vertical central axis parallel to the vertical edge of each of said at least four rotor blades, said central axis extending through the center of said datum sphere; and a space between said vertical central axis and said vertical edge of said revolute surface on each of said at least four rotor blades; and each of said at least four rotor blades having a surface perpendicular to said revolute surface, engaged along said edge that lies on the surface of a datum sphere, said surface being coincident with said datum sphere; and each rotor blade in said rotor assembly having a semi spherical vertical cross section; wherein fluid flowing over one of said at least four rotor blades flows through said space between said vertical central axis and said vertical edges and then flows over another of said at least four rotor blades, exerting a force on each, and said fluid is compressed by said surfaces perpendicular to said revolute surfaces as the fluid exits the rotor assembly at a higher velocity than the ambient flow. 